6 foods that you should never reheat in the microwave

There are a number of foods that you should never reheat in the microwave, as they could actually end up making you sick.Shutterstock/Kostenko Maxim

The INSIDER Summary:

• It's generally fine to reheat foods that were refrigerated.
• If a food cools to room temperature and then gets reheated, botulism can grow.
• Heating breastmilk in the microwave can cause hotspots. Heat it in a stovetop hot water bath.

It's great to have food left when you go out to eat or when you cook at home, and most of us just stick it in the microwave without much thought. There are a number of foods that you should never reheat in the microwave, as they could actually end up making you sick. Even if you've managed to be fine thus far, it's helpful to know for the future so you don't end up struggling over the toilet.

"Eating leftovers can be a healthy and cost effective way to make the most of your food," says Brigitte Zeitlin, RD over email. "But there are some foods that can be dangerous to reheat, especially if they weren't stored properly (in an airtight container and at the right temperatures) beforehand."

For many of these foods, it's not just the microwave that poses problems, but the changes in temperature that happens when you leave them out and then consequently reheat it. Either way, you're better safe than sorry. Next time you want to eat what's left in your fridge, you might want to be careful and avoid reheating these six foods in the microwave, as they could be hazardous to your health.

1. Potatoes

"Potatoes can lead to food poising when being reheated if they were initially left to cool at room temperature after being cooked the first time," says Zeitlin. "By letting them cool at room temperature, a bacteria called botulism can grow, so it is best to refrigerate your potatoes directly after cooking them if you do not intend on consuming immediately." Reheating them after they have been cooled in the refrigerator will not cause any issues.

2. Chicken

Karen Mordechai

It's OK to reheat chicken once if it has been cold, but be wary of putting it in the microwave, unless you're certain it can cook evenly all the way through. "The inside should be piping out," says Zeitlin. Microwaves can sometimes cook food unevenly, which means there could still be bacteria remaining on the chicken if it's not thoroughly cooked.

3. Rice

If your rice is left standing at room temperature, it can contain spores of bacteria that can multiply and cause food poisoning, according to the National Health Service (NH)S. Microwaving it won't kill the bacteria, so you're best eating your bowl of rice in one setting, or refrigerate it right away, which would make it okay to reheat later.

4. Mushrooms

"Mushrooms are another vegetable not to reheat," says Zeitlin. "Mushrooms can cause stomach upset when reheated due to the micronutrients in them, so again, it is best to finish your mushrooms the first time around." Bacteria can also grow on mushrooms if they're left out at room temperature.

5. Foods With A Lot Of Oil

All oils can withstand varying levels of heat, but if that level is exceeded, it produces toxic fumes and hazardous substances called free radicals that can cause issues such as cancer, according to Livestrong. Avoiding reheating oily foods in the microwave, as they could get too hot and burn.

6. Breast Milk

If you have a baby, avoid reheating any breast milk in the microwave, as studies have shown that microwaves heat baby's milk and food unevenly, resulting in "hot spots" that can burn your baby's mouth and throat, according to the FDA. "Err on the safe side and heat any 'milk' you are feeding your infant in a hot water bath on the stove," says Susie Garcia, RDN over email.

In general, when reheating foods, make sure they cook at high temperatures, and don't eat any leftovers older than three days to help make sure the food is still safe to eat and no bacteria or mold has grown on them.